The present invention relates to a stepping motor and a method of manufacturing the stepping motor.
In a related art stepping motor, a stator is bonded to an inner surface of a motor case, and a bearing is fixed to the motor case. (Refer to, for example, the patent documents 1 to 3). FIG. 11 is a sectional view of such a related art stepping motor. Referring to FIG. 11, a magnetic field is generated in magnetic pole teeth of yokes 104a, 104b, 108a, 108b owing to a pulse voltage applied to coils 105a, 105b wounded around a rotor magnet 107 coaxially therewith. A driving force is generated owing to a magnetic field of the multi-pole magnetized rotor magnet 107, and a shaft 101 and rotor magnet 107 are rotated in a body.
The yoke 104a includes a motor fixing stay 103 secured thereto, into which a bearing member 102a is press-fitted firmly. On the other hand, the yoke 104b includes a disc type bearing fixing member 106 secured thereto. A bearing member 102b is press-fitted into the bearing fixing member 106. The shaft 101 is supported by these bearing members 102a, 102b. 
Patent Document 1
JP-A-06-098520
Patent Document 2
JP-A-10-084663
Patent Document 3
JP-A-02-218072
In the construction of the above-described related art stepping motor, the bearing fixing member 106 is used only for fixing the bearing member thereto, and a total length of the motor is long by a length corresponding to the thickness of this bearing fixing member 106. In other words, a ratio of the length of a magnetic circuit to a total length of the motor is small due to the existence of the bearing fixing member 106. The number of parts increases correspondingly to the provision of the bearing fixing member. Moreover, since the bearing fixing member 106 is secured to the yoke 104b, the man-hour increases, and this hampered the improvement of the productivity of the motor.
In order to solve these problems, the use of a method of fixing the bearing member 102b directly to the yoke 104b is conceivable. However, in a structure in which the bearing member 102 is simply press-fitted into the yoke 104b, a high fitting accuracy is demanded between the bearing member 102 and yoke 104b. Further, a high processing accuracy is demanded with respect to the bearing member and yoke for the purpose of centering the shaft. This causes the improvement of the productivity of the motor as a whole to be hampered. In the fixing method using a press-fitting operation, the bearing member is liable to be loosened due to an impact and heat, and the possibility of occurrence of slip-off of the bearing member is comparatively high. Therefore, this method has problems concerning the durability and reliability of the stepping motor.
In a related art method of simply fixing a bearing member to the yoke, an opening of the yoke cannot be sealed, so that dust readily enters the interior of the motor. Therefore, this method also has problems concerning the durability and reliability of the stepping motor.